DESCRIPTION: This proposal intends to follow a group of 117 adolescents with ADHD and a comparable control group for as well as over 100 of their siblings, subjects already followed for five years, for an additional five years. Given the mean age of the sample, this study will provide information about ADHD as subjects mature from adolescence into young adult life. These subjects will be assessed on six domains: psychopathology, cognitive-neuropsychological functioning, school dysfunction, adaptive functioning, treatment interventions and psychosocial adversity. A variety of measures are included in the assessment of each domain. Analytic methods address six issues: variable age of onset of psychiatric illness; nonindependence of observations within families and between time periods; effects of treatment; integration of information across multiple informants; effects of confounding variables; wide age range of the sample at baseline. The investigators will test three general hypotheses: prediction of outcome based on baseline ADHD (or sibling of ADHD); prediction of outcome based on comorbidity; prediction of outcome and comorbidity based on DSM-IV subtypes.